1. Field of the Invention
The present invention relates to a technique for measuring surface form of an object and also relates to a technique for measuring a stress in a film formed on an object with use of measured surface form.
2. Description of the Background Art
In manufacturing a semiconductor device, conventionally, various processings such as a film deposition or an annealing process on a semiconductor substrate (hereinafter, simply referred to as “substrate”) are performed, and a residual stress occurs in a thin film on the substrate due to these processes. In recent, with high definition of the semiconductor device, the residual stress greatly affects the quality of the semiconductor device to increase the necessity of measurement of the stress in the thin film.
As one apparatus for measuring a stress in a thin film in a noncontact manner, Japanese Patent Application Laid-Open No. 2000-9553 (Document 1) discloses a thin film evaluation apparatus for measuring a radius of curvature of a substrate by an optical lever detection method to obtain a stress in a thin film with use of the measured radius of curvature. In the thin film evaluation apparatus of Document 1, a laser beam emitted from a laser light source moves on the substrate, reflected lights reflected on the thin film are received on a detector and reflection angles in a plurality of positions on the thin film are calculated on the basis of receiving positions on the detector, to thereby obtain the radius of curvature.
Japanese Patent Application Laid-Open No. 2004-138519 (Document 2) discloses a film thickness measuring apparatus for measuring a thickness of a film formed on an object, where a light shielding pattern is positioned on an optical path of an illumination light which is emitted from a light source to the object, an image of the light shielding pattern is formed on the optical path of a reflected light reflected on the object, and a tilt angle of the object is obtained on the basis of the image. In the film thickness measuring apparatus of Document 2, a thickness of the film formed on the object is obtained with use of the obtained tilt angle, thereby achieving a high accurate film thickness measurement.
In the thin film evaluation apparatus of Document 1, since the laser beam is used for measurement of the radius of curvature, when a reflectance of a measurement object to a wavelength of the laser beam is low, measurement errors of the radius of curvature become large and it is not possible to obtain the stress in the film with high accuracy. In a case where a pattern is formed on a substrate, since the laser beam is scattered because of the pattern and the radius of curvature cannot be obtained with high accuracy, the apparatus of Document 1 is less suitable for stress measurement of the substrate on which a pattern is formed.
Further, in the apparatus of Document 1, since the radius of curvature is obtained on the basis of the shifts of the receiving positions on the detector of the reflected lights reflected on the plurality of measurement positions and a focusing position in each measurement position greatly affects a measurement result, a high accurate focusing has to be performed in each measurement position. As a result, the construction of the apparatus is complicated to increase a time period for stress measurement.